This invention relates generally to apparatus for producing high-intensity-discharge arc tubes and, in particular, to an apparatus for automatically tipping-off such an arc tube.
A number of methods and apparatus for the tipping-off hermetically sealed vitreous bodies such as lamps, radio tubes and other electrical devices having vitreous envelopes provided with exhaust tubes which are sealed or tipped-off after the envelope has been evacuated, have been described. One such apparatus is in U.S. Pat. No. 2,496,303, dated Feb. 7, 1950, issued to R. O. Morse et al. The Morse patent discloses a method of tipping-off an exhaust tube which entails coating the portion of the exhaust tube closest to the vitreous envelope with graphite at the point where the tip is to be trimmed after tipping-off to avoid undue heating of the envelope. A circumferential cut is made at the trim point and the remaining exhaust tubulation is broken off. The graphite also aids in preventing glass from coating any lead-in wire that it is to extend beyond the tip-off.
In U.S. Pat. No. 2,983,078, dated May 9, 1961, issued to G. R. Mistler et al. is disclosed a method of sealing a vitreous conduit such as an incandescent-type lamp having an exhaust tubulation. The method entails preheating the tubulation in the area next to a heat sealing member. A spring urges the sealing member in a clockwise direction causing the member to effect considerable stress on the heated tubulation and the temperature of the tubulation is such that the stress applied by the heat sealing member causes a substantial deformation of the tubulation and permits the heat sealing member to pass through the tubulation thereby effecting the seal.
In U.S. Pat. No. 2,764,857, dated Oct. 2, 1956, issued to G. F. Schaefer is disclosed a method of tipping-off an exhaust tubulation which method entails heating the tubulation at the point desired for the end of the tip-off with a pointed gas flame to effect the tip-off.
In U.S. Pat. No. 3,188,788, dated June 15, 1965, issued to C. Wiener et al. is disclosed a tipping-off apparatus compatible with an automatic exhaust machine. The tipping-off apparatus includes means for holding the arc tube in predetermined alignment relative to a striker arm. An annular tipping-off burner substantially encircles the exhaust tubulation at a predetermined point. The burner heats the tubulation and then the striker arm is activated thereby effecting the tip-off.
It has been found that the tip-off apparatus of the prior art does not readily adapt to high-speed automatic arc tube fabricating machinery.